It is known in the art that various subsea assemblies are applied in the exploration and production of hydrocarbons such as oil and gas. These include complex installations with various equipment and assemblies. Such assemblies may be X-mas trees, BOPs, production manifolds and so on, as known to persons skilled in the art.
Small and large scale leakages of hydrocarbons and other undesirable materials such as injecting fluids and chemicals are known to occur from such subsea assemblies, particularly during production, resulting in discharge of hydrocarbons or other chemicals to the surrounding water.
Environmental impact analysis of hydrocarbon leakage is today a matter of concern all over the world. Hence, hydrocarbon exploration and production agencies are now attaching immense importance on regulating and substantially preventing hydrocarbon and other leakage from subsea units, not only from economic points of view, but in particular due to environmental concerns.
In the above context, it is hereby clarified that hereinbefore and hereinafter, the present invention as well its technical background, prior art already known, are explained with reference to hydrocarbons, X-mas trees, production units/equipments. It should be understood that these are all limitations for the sake of explanation. The present invention pertains to all types of leakage detection under water such as hydrocarbons, hydraulic fluids and chemicals and so on. Further, the present invention is applicable in respect of all types of units, installations, equipment and subsea assemblies such as X-mas tree, production manifolds and so on, as known to persons skilled in the art, involved in hydrocarbon recovery by offshore operations. Reference to subsea hydrocarbon production units and operations, is purely exemplary and non-limiting.
Application of acoustic methods for subsea leak detection has found applicability for quite a long time, but has suffered from the disadvantage of sensitivity to shadowing of signals by subsea structures and units. However, it is known that such disadvantages are effectively overcome by deploying a plurality of leak detectors around potential leakage zones.
Biosensors, depending on study of the behaviour of the aquatic animals to pollution are known to be effective at shallower levels. However, such sensors are now mainly under experimentation.
Capacitive sensors measure the change in dielectric constant of the medium surrounding the sensor and are found to be fairly and reasonably reliable in precise detection of hydrocarbon and other leakages from subsea production units.
Prevention of hydrocarbon leakage of any scale during subsea production has become increasingly more important. The earlier a small leak can be detected the easier it will be to prevent any major leakage. A significant problem encountered in this respect is toe position the leak detector so that it will correctly detect a leakage.
Proper positioning of the leak detection system is required not only for precise detection of leakage, but also for ensuring that detection of natural seepage from the sea bed does not trigger the leak detector. Natural seepage may trigger wrong signals to the leakage management team. Further, retaining the position of the leak detector after it has been installed is another challenge.
In other words, the leak detection systems known in the art are not suitably adapted to be precisely and securely positioned.
U.S. Pat. No. 7,918,126 discloses a leak detection system for precise detection of leakage of subsea materials such as hydrocarbons, hydraulic fluids, chemicals. It includes a plurality of sensors and a controller for receiving leak detection data from such sensors. It directs the sensing activities of the sensors, based on the data. However, it does not teach precisely and securely location of the system for leak detection, because it is not adapted to be so positioned and moreover it involves complex constructional network.
Similarly, U.S. Pat. No. 4,282,487 discloses a hydrocarbon detection system, but here again is not disclosed how the system is adapted to be precisely and securely positioned for precise detection of leakage. Rather, it generally states under “Background of the invention” that it is desirable that a plurality of detection units should be located at potential locations of hydrocarbon escape.
To take care of the concerns as stated in the preceding paragraphs, it has been common knowledge that leak detection systems are often located in the ceiling of subsea assemblies such as X-mas trees. The motive is to arrest all leak detections coming out from such units. However, such positioning results in faulty detection, in as much as leakage of hydrocarbons such as oil and gas above the X-mas tree are not detected.
Further, the construction of such prior art leak detection systems does not allow for suitable and secure location for precise detection. Additionally, due to their constructional disadvantage, prior art subsea leak detection systems cannot be easily installed, or for that matter retrieved after installation, for maintenance or replacement. This is for example, due to the limited space between the X-mas tree roof and X-mas tree, the desired location of installation.
Accordingly, there is a need for a subsea leak detection system, which by virtue of its simple construction is adapted to be suitably and securely located/installed for precise detection of leakage of hydrocarbons.
The present invention meets the above long felt need and other associated needs as will be clear to persons skilled in the art from the following.